a. Field of the Invention
This invention relates to a control unit for thermal conditioning systems required to cool or heat one or more building spaces, and is of the type used where an air-conditioning plant or heat-emitting system has been off for a period and has to start again in time for the space to attain a desired temperature by a predetermined time, said control unit being started by a control clock.
B. Prior Art
In buildings not in heated use 24 hours or all days of the week it is possible to save energy by lowering the temperature during the time intervals when the buildings are unoccupied.
Savings may be achieved by partly turning off the heating, ventilation and pumping plant.
After such a reduced operation of a thermal conditioning system, stepped-up operation of the thermal conditioning system will be required some time before the building is to be occupied.
Time intervals, i.e. the time from the start of the system until the desired temperature is attained in the building, vary greatly in accordance with the circumstances, such as the outside temperature, wind-velocity, sunlight, inside temperature, humidity of the air and the constants of the building, such as insulation, specific heat, external and internal heat-conductors, air change, the temperature of the walls, the capacity of the thermal conditioning system etc.
For starting the thermal conditioning system, various control units have been suggested that take at least some of these parameters into consideration, so that start of the system takes place as late as possible, thereby saving as much energy as possible and still securing a satisfactory climatic condition of the building at a predetermined time, for instance at the beginning of working hours.
Most of the units of this type operate according to linear principles or graphic programming and a voltage is built up according to predetermined temperatures and compared with electronically or mechanically predicted values obtained over a time interval corresponding to the earliest possible time of starting, for instance 4 to 8 hours before the building has to reach the required comfortable climatic condition.
In British Pat. No. 1,193,711 such a control unit for thermal conditioning systems is described. In this unit, the time of starting is determined on the basis of the inside temperature and the outside temperature, while the above-mentioned conditions and the constants of the building, the building rooms or spaces as well as the temperature of the building elements are not taken into account.
Due to the above-mentioned conditions, such a control unit will make miscalculations when there are major fluctuations of temperature, especially in buildings where the building elements have several thermal time constants of importance.
The operation of such a unit may to some extent be satisfactory, provided the intervals of non-operation are of equal duration, and sufficiently short so that the building does not cool down to the low maintenance temperature. If there are longer intervals of non-operation, for instance during a weekend, the walls of the building and the existing equipment will be cooled still more, and therefore it will take longer to heat up the building to the desired temperature. Because of this fact, the prior unit cannot calculate the correct time for starting the thermal conditioning system on the basis of the inside and outside temperature alone. This fact is so widespread a phenomenon of the hitherto known control units that within this field this condition is in everyday speech called the "monday phenomenon". If the control unit is adjusted to fit certain conditions, the system will not work under other conditions, as it makes miscalculations when the wall and other heat-consuming parts cool even more during weekends, holidays and the like.